The invention concerns a process for producing an elastomer substrate web.
The process for producing an elastomer substrate web known from the prior art usually comprises a customary calendering process, in which a polymer mixture is passed from an internal mixer either via a breaking mill with a conveyor belt or a conveying extruder to a calender.
In the said calender, an endless, uniform polymer web is produced by using considerable energy (mechanical and thermal). This polymer web is drawn off the last forming roller by means of one or two driven shafts and is passed via chilling rollers and/or a chilling belt to the wind-up.
In the winding-up station, the polymer web is provided with a release agent, whether a powder or an intermediate substrate in web form with good release properties, such as a PE film for example. Finally, winding into a bale takes place.
FIG. 1 shows a graphic representation of the known process.
According to this known process, the polymer mixture 1, prepared in a mixer which is not represented in any more detail, is fed via the mill 10 to a calender 20, formed by four rollers, in which the polymer mixture 1 is formed out into a web 2. The web 2 is passed on via further rollers into the cooling station 30. Upstream of the winding station 40, the auxiliary substrate 3 is placed onto the web 1.
This process has proven successful for classic polymer mixtures.
However, the process described above fails in principle when forming out polymer mixtures with strong inherent tack and/or with low strength in the uncrosslinked state, to be precise because the polymer web cannot be drawn off the last forming roller without the web tearing, or only if it stretches severely.
For mixtures with strong inherent tack and/or with low strength in the uncrosslinked state, therefore only coating by means of a nozzle has been possible until now,
The object of the invention is to provide a process which makes it possible to process polymer mixtures with high inherent tack and/or low strength on conventional calenders without any loss in efficiency or product quality and without additional complex modifications.
This object is achieved by a process as set out in the main claim. Advantageous embodiments of the same are the subject of the subclaims.
Accordingly, the invention concerns a process for producing an elastomer substrate web, comprising the following process steps:
a) feeding in a polymer mixture, in particular into a mixer,
b) conveying the ready-prepared polymer mixture to a calender, comprising at least two rollers,
c) forming the polymer mixture out in the calender into a web,
d) applying an auxiliary substrate in web form by means of a pressure-exerting roller, which is in contact with the last forming calender roller, for receiving the web, and
e) if appropriate, cooling, crosslinking and/or winding up the web located on the auxiliary substrate.
The auxiliary substrate can completely absorb the drawing-off stresses occurring at the calender roller, so that the actual product is not subjected to any stressing. In a preferred embodiment, the auxiliary substrate comprises commercially available films, papers or woven fabrics, if appropriate with release properties specifically set to suit the product, so that it can be removed again without any problem during further processing.
In addition, the auxiliary substrate may be used for the building up of multi-layer systems, in that it is provided with one or more layers on conventional coating installations. These layers may be, for example, colour, barrier. primer and/or adhesive layers.
The process according to the invention also offers the possibility, by application of the auxiliary substrate on both sides, of providing the polymer web with one or more layers on both sides. If appropriate, for this purpose the auxiliary substrate must be provided with an additional release film, in order to avoid blocking of the layers. The auxiliary film should then be uncovered before applying to the polymer web.
The polymer mixture is preferably chosen from the group of natural rubbers or synthetic rubbers or it comprises a two-component blend of natural rubber/synthetic rubber or two synthetic rubbers.
Furthermore, the synthetic rubber or the synthetic rubbers is or are preferably chosen from the group of randomly copolymerized styrene-butadiene rubbers (SBR), butadiene rubbers (BR), synthetic polyisoprenes (IR), butyl rubbers (IIR), halogenated butyl rubbers (XIIR), polyacrylate rubbers (ACM), ethylene-vinyl acetate copolymers (EVA) and polyurethanes.
Furthermore, the polymer mixture may contain additives such as fillers, antioxidants, plasticizers and adhesive resins.
All adhesive resins previously known and described in the literature can be used as tackifying resins. Mentioned by way of example are colophony resins, their disproportionated, hydrated, polymerized, esterified derivatives and salts, aliphatic and aromatic hydrocarbon resins, terpene resins and terpene phenolic resins. Any desired combinations of these and further resins may be used in order to adjust the properties of the resultant adhesive compound according to desired requirements. Reference is made expressly to the description of the current state of knowledge in the xe2x80x9cHandbook of Pressure Sensitive Adhesive Technologyxe2x80x9d by Donatas Satas (van Nostrand, 1989).
All plasticizing substances known from adhesive tape technology can be used as plasticizers. These include, inter alia, paraffinic and naphthenic oils, (functionalized) oligomers such as oligobutadienes, oligoisoprenes, liquid nitrile rubbers, liquid terpene resins, vegetable and animal oils and fats, phthalates, functionalized acrylates.
For the purpose of thermally induced chemical crosslinking, all the previously known thermally activatable chemical crosslinking agents, such as accelerated sulphur or sulphur-onor systems, isocyanate systems, reactive melamine, formaldehyde and (optionally halogenated) phenolic formaldehyde resins or reactive phenolic-resin or diisocyanate crosslinking systems with the corresponding activators, epoxidized polyester and acrylic resins as well as their combinations can be used in the case of the process according to the invention.
The crosslinking agents are preferably activated at temperatures in excess of 50xc2x0 C., in particular at temperatures from 100xc2x0 C. to 160xc2x0 C., most particularly preferably at temperatures from 110xc2x0 C. to 140xc2x0 C.
The thermal activation of the crosslinking agents may also take place by means of IR rays or highenergy alternating fields. The crosslinking of the polymer mixture may, furthermore, take place by means of a combination of ionizing radiation and chemical crosslinking agents.
The thickness of the web downstream of the calender is, in particular, between 100 xcexcm and 4000 xcexcm, in particular 400-2500 xcexcm. The auxiliary substrate has, in particular, a thickness of between 10 xcexcm and 2000 xcexcm, preferably between 15 xcexcm and 150 xcexcm.
The process can be used particularly advantageously for producing a web from a hot-melt adhesive compound on the basis of non-thermoplastic elastomers.
Surprisingly, it was found that, by the use of auxiliary substrates, a high bonding strength can be achieved in multi-layer systems without an additional processing step and an unusually good constancy of thickness can be achieved, unattainable by conventional forming out with the polymer mixtures described.
The process according to the invention is to be described in more detail below by means of a further figure and on the basis of several examples, without wishing to restrict the invention unnecessarily. In the drawing: